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Dynamics of Inverse Metal Oxides on Metals Catalysts using Spectro-Kinetics: Reversible Brønsted Acid Site Formation and Irreversible Reduction
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DOI：10.1039/D5CY00917K.png)
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Abstract
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Brønsted acid sites (BAS) in inverse catalysts are vital for the selective hydrogenolysis of polyols; specifically cleaving secondary C-O bonds. These BAS form dynamically in situ in a H2 environment. While H2 enables rapid BAS generation on short timescales; it reduces the catalyst at prolonged exposures. The active center for BAS generation; the kinetics of BAS formation; its reverse decomposition; and the irreversible oxide reduction have lacked direct experimental evidence. Here; aided by advanced spectro-kinetic studies; we identify trimeric W3Ox sites on Pt as the active centers for BAS generation; whereas isolated WOx species on SiO2 act merely as spectator species; demonstrated using an inverse WOx/Pt catalyst as a representative system. A detailed kinetic profile capturing the dynamics of W3Ox sites on Pt is also established. The rate constant for BAS formation is two orders of magnitude higher than for its decomposition; which is one order of magnitude faster than the irreversible site reduction. Co-fed H2O suppresses the site reduction by ~ 50%. Furthermore; the H2 partial pressure plays an important role. While lower gas-phase H2 partial pressure does not influence the reversible BAS formation; it can significantly (~ 3x) suppress catalyst reduction. These findings offer critical insights into optimizing reaction conditions through periodic H2 pulsing; enhancing catalyst stability and performance in hydrogenolysis reactions.
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